The present invention relates to a golf ball excellent in flight characteristics.
As is well known, to improve flight characteristics of a golf ball, that is, to obtain the largest travel distance of the ball hit with a golf club, it is important to increase the resilience of the ball and to reduce the air resistance during flight caused by dimples arranged on the outer surface of the ball. With respect to the latter factor, from the viewpoint of reducing the air resistance caused by the dimples, various attempts have been made to improve the shapes of the dimples, to improve the arrangement of the dimples so as to distribute the dimples as uniformly and densely as possible, and to obtain the optimum ratio of dimple volumes to the total volume of the ball.
The shape of a dimple in a plan view is generally circular, and the shape of a dimple in a cross-sectional view is generally selected from various kinds of shapes. The first cross-sectional shape of the dimple is a nearly circular-arc shape as a whole. To be more specific, as shown in the cross-section of FIG. 6, an outline, extending from both edges to a bottom portion via side walls, of a dimple is formed by a circular-arc defined by a curvature radius “f” and the center positioned outside the golf ball. In the figure, reference numeral 1 denotes the golf ball, 2 is the dimple, 3 is the edge of the dimple, 4 is the side wall of the dimple, and 5 is the bottom portion of the dimple, and further, character “O” denotes the center of the golf ball, “R” is the radius of the golf ball, “f” is the curvature radius of the wall surface of the dimple 2 the center of which is “P” positioned outside the ball, and “i” is the depth of the dimple.
The known second cross-sectional shape of the dimple is a double shape composed of a combination of a large circular-arc and a small circular-arc. In general, the side wall portion is formed by the large-circular arc and the bottom portion is formed by the small circular-arc. The third cross-sectional shape of the dimple is configured such that the bottom portion is formed into a shape similar to that of the bottom of a pot or a shape similar to that of a caldera. The caldera shape is a modification of the double shape, wherein the bottom portion formed by a small circular-arc projects outwardly from the ball.
Nevertheless, it has been expected yet to obtain more desirable flight characteristics of a golf ball by improving the shapes of dimples.